1. Field of the Invention
This invention relates to aluminum extrusions and methods of makings same and, more specifically, to aluminum extrusions having multiple thermal brakes and a method of making same.
2. Brief Description of the Prior Art
Aluminum extrusions having a single thermal brake are well known in the art. A typical extrusion with a single thermal brake is shown in the patent of Nilsen (U.S. Pat. No. 3,204,324), the disclosure of which is incorporated herein by reference, wherein two portions of the same extrusion are joined by a bridge therebetween which forms a part of the original extrusion. The bridge maintains the desired dimensional relationship between the two extrusion wall portions to very accurate tolerances during further processing. The bridge forms a wall portion of a chamber into which is poured a hardenable or settable thermal braking material which has very low thermal conductivity. After the hardenable material has set within the chamber, the bridge is broken so that the two extrusion portions are coupled together only with the thermal braking material to provide thermal insulative properties between the two extrusion portions. Extrusions of this type have found great acceptance, particularly in conjunction with the construction of windows, where thermal insulation from the exterior to the interior of a building is necessary.
More recently, aluminum extrusions have been developed which include a pair of thermal braking elements therein, each thermal braking element being disposed in one of two bridge or spacer elements supporting opposing walls of the extrusion. The pair of spacer elements with thermal braking elements is required to provide support and insure that dimensional tolerances are maintained between the opposing extrusion walls while also providing the required thermal isolation between the opposing walls after completion of fabrication.
To provide the pair of thermal brakes in a single member, one form of prior art has utilized two separate extrusions with a pair of preformed thermal insulators which are force fitted into grooves therefore in each of the extrusions. The final product with two thermal brakes fabricated by this procedure has difficulty maintaining dimensional tolerances and is relatively expensive to manufacture due to the requirement of two separate extrusions and a custom fabricated thermal insulating element which is manually inserted into grooves in both extrusions.
Another form of prior art extrusion with two thermal brakes therein provides a pair of chambers, one in each bridging element, one of the bridging element having a pair of extensions or receivers spaced from and beneath the chamber for carrying a rigid vinyl member therein. The above described procedure of Nilsen is used to form a first one of the thermal brakes in one of the chambers. The liquid thermal braking material is poured into one of the two chambers and permitted to set therein. Then a portion of the bridge material is removed from the chambers for both of the thermal brakes prior to pouring of the liquid thermal braking material into the second chamber because it is difficult to sever the bridge material of only one of the bridges. It follows that, with both of the bridges severed, the second chamber no longer has the continuous bridge so the liquid braking material cannot be retained in the second chamber if now poured therein. This problem has been alleviated in the prior art by placing a rigid vinyl strip insert over the extensions or receivers and beneath the severed portion of the chamber or break in the bridge material of the second chamber to close the break therein and permit the liquid braking material to be poured into the second chamber and set therein.
A problem with this procedure is that the extrusion are quite long, usually on the order of about 18 feet in length, thereby making the cost of placing the rigid vinyl strip in the channel beneath the severed region of each extrusion economically prohibitive. This is due to the fact that the rigid vinyl strip (stop gap material) must be held to tight manufacturing tolerances in order to fit into the chamber without binding or jamming along the length of the aluminum extrusion or conversely without being too loose to eliminate leakage of thermal braking material into the main chamber of the hollow aluminum extrusion. For the same reasons, the receivers of the vinyl strip in the aluminum extrusion itself must be held to strict, better than standard, tolerances to be able to accept the vinyl strip prior to filling with thermal brake material. Also, this arrangement results in weak extrusion elements which leads to premature breakage. Furthermore, the removal of a portion of the bridging element in one of the thermal brake material holding chambers either during extrusion or prior to incorporation of the thermal braking material into either of the chambers, permits the extrusion walls to rotate about the one bridging element and providing a problem of dimensional tolerancing. It is therefore apparent that a less costly procedure and improved multiple thermal brake extrusion is highly desirable.